Christian fiction is a red flag for me (except for novels based on Biblical history, which is a bit of a hobby. And, of course, doesn't count as Christian because most of them are Old Testament).

Bad book covers - yep, me too. If the author/publisher can't be bothered to sort out a decent cover, presumably they can't be bothered to sort out a decent novel either.

Pirates. I refuse, absolutely, to read a book with pirates in it. Unless they are being successfully hunted down by the lawful authorities.

Love triangles composed of kick-ass heroine and two incredibly hot males. Done to death lately. I now tend to assume that any book/series with this plot device is going to be a rip-off of something else, or some kind of formulaic crap.

Anything where the heroine gets pregnant by accident, set after the 1960s. Contraception, ladies. Any woman who doesn't respect herself enough to take precautions gets no respect from me.

Any book where the female lead has got herself into a difficult situation entirely through her own stupidity and needs a man (usually a rich, gorgeous one) to rescue her.

Any blurb that doesn't describe the book. No description, no purchase. No pigs in pokes for me.